I am considering building a copper coil heat exchanger inside of a converted keg/boil pot. I was just wondering if anyone has any experience building one or if there are any plans on the internet for such a contraption? I'm looking for what types of fittings to use, piping, etc...

I think most people use 1/2" copper. I've seen people use bulkhead attachments to the keg. I still don't know why people wouldn't just make it like an immersion chiller and save have to drill holes in the keggle, plus you can always remove it at a later date.

Yeah I am also curious if it is indeed worth putting together a set up with a built in heat exchanger or just go with an immersion chiller. Drilling holes for bulkhead attachments is really not my concern. Just seems that having a HLT with a built-in heat exchanger would be efficient. Thoughts?

They both will perform the same. I prefer to use my 50' 1/2" copper IC for heat transfer and for chilling. It's easy to insert and take out of the kettle without dealing with wrenches and fittings. Would be easier to clean as well. I also built a 50' 1/2" SS exchanger into a home made lid for my 30 gallon kettle. Its connected to the top with a couple swedgelock fittings connected to the lid. That setup works real good too, and I use it on my 20 gallon batches for the heat exchanger and for the chiller. I can put it in and take it out fairly easy, and it is easy to clean as well. I have a couple of pics on my blog if ya want to check it out. Blog url is under my profile.

My setup is a bit different than most, but I am always changing it. I mostly use the BIG equipment when I have a recipe nailed down and I want to produce more than the usual 5 or 10 gallons. When I do brew a 20 gallon batch, I usually have my brew buddies over and they pitch in for the cost of brewing...then we split up the batch among us and ferment on our own...using different yeasts...then we get together to compare results. It's always a surprise to us when we do that. I'll also brew up a BIG batch if we're attending any local brew competitions and such. (BIG BREW DAY IS COMING)

Otherwise, I normally brew 5 gallon batches for recipe formulation reasons, and on occasion i'll do a 10 gallon batch if i'm expecting any company.
The ASCO Valve works great and it is the heart of the HERMS system. I control it via RANCO Temp controller while recirculating the wort during mashing. I set the controller to 4 degrees above the desired mash temp and recirculate continuously....it works like a charm!

Like I stated....i am always changing my system and trying new methods...ever since I started to batch sparge (from fly sparging)...(blame bill..LOL), I have found that I currently need to change a few things to make the process a little simpler...i just have to get out there and change it....

Did you happen to view the schematic of the system? There is a drawing there which describes the plumbing....BTW...it's not as bad as it looks and is real easy to operate, and it takes me the same time to brew 20 gallons as it does 10. My last 20 gallon batch took 8 hrs, with the most time consumed by waiting for the small pump to transfer the hot liquor from the kettle to the HLT (cooler). I have since picked up a larger centrifugal pump and can now pump my hot water at approx 10 gallons a minute. It now takes me 3 minutes to pump my sparge water from the kettle to the new large cooler that I use now. 108 qt cooler. I have it plumed with Tri-Clover fittings and is real easy to set up. I also plan to use the new pump for a whirlpool too. I have yet to test this out, but I have confidence that all will be well, and that my brew day will be shortened considerably by using the new pump.

while mashing, the wort is circulated thru the coil in the kettle which is filled with hot water held at a temperature at approximately 3 - 4 degrees higher than the desired mash temp. the kettle has a thermowell mounted to the cover, and the temp probe is inserted to read and control the temp of the hot liquor. The kettle burner is controled by the temp controller by opening the ASCO valve when heat is needed, and the valve closes and shuts down the gas when the desired temp has been reached. This is what maintains the mash temp to +/- 1 deg of your desired mash temp. I can very easily perform any step mash program with this setup if desired.

Once the mash is converted...I then pump the hot liquor from the kettle, to an insulated cooler....shut down the temp prob as it is no longer needed,,,remove the lid and the coil thats attached....after draining the kettle of all hot water, the sparge cycle is initiated...whether it's a fly sparge or batch sparge and the wort is collected into the kettle....once filled with wort...the boiling of the wort starts....and hops are added etc..

When the boil is finished, the cover and the attached coil is placed back into the kettle, and the chilling stage begins....i start it by using my house water to chill the wort down to around 125 deg F...then switch the plumbing and run my sub-pump in a cooler filled with ice and water. The ice water is pumped thru the coil and chills the wort down quickly to my desired pitching temperature. I usually get the wort about 60 degF...whirlpooling while chilling...then transfer to my primary fermenter....aerate...then pitch the yeast.

I hope this explains it a little better as only 1 coil is used for these 2 separate processes.